MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1249 PM EDT FRI AUG 29 2014 VALID AUG 29/1200 UTC THRU SEP 02/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM DEEMED SIGNIFICANT ENOUGH TO IMPACT ITS FORECAST. MEANWHILE...THE 12Z GFS SEEMS TO SLIGHTLY UNDERPLAY THE MOISTURE CONTENT ALONG THE WESTERN GULF COAST WITH VALUES OFF BY ABOUT 0.25 TO 0.35 INCHES. ...VORTICITY MAXIMA LIFTING THROUGH THE LOWER MS VALLEY ON SATURDAY... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS WITH THE 00Z ECMWF/UKMET FORECAST CONFIDENCE: AVERAGE A BROAD AREA OF DEEP CONVECTION OVER THE WESTERN GULF OF MEXICO IS OCCURRING IN RESPONSE TO SEVERAL VORTICITY MAXIMA LIFTING NORTHWARD TOWARD THE GULF COAST. THE ENERGY AND ASSOCIATED ENHANCED MOISTURE CONTENT WILL EVENTUALLY WORK THEIR WAY INTO THE LOWER MS VALLEY BY THIS EVENING. THE MYRIAD OF SHORTWAVES SHOULD GRADUALLY CURL ALONG THE WESTERN EXTENT OF AN UPPER RIDGE ANCHORING THE EAST COAST. THE 12Z NAM IS MORE AGGRESSIVE AT KEEPING SOME ADDITIONAL ENERGY LOCKED AGAINST THE WESTERN GULF COAST LATE SATURDAY. LOOKING AT OTHER MODELS...THE 00Z CMC IS PROBABLY THE STRONGEST ALOFT AS IT CARRIES A COMPACT SHORTWAVE THROUGH THE OH VALLEY ON SUNDAY MORNING WHILE THE 12Z GFS AND 00Z ECMWF/UKMET ELONGATE THE ENERGY. THE LATTER THREE VARY A BIT IN TIMING WITH THE 12Z GFS BEING QUICKER THAN THE 00Z ECMWF/UKMET. WILL GO AHEAD AND FAVOR A MIX OF THESE AS THEY DO ALL SHOW A VERY SIMILAR EVOLUTION. ....SHORTWAVE ENERGY MERGING WITH THE NORTHERN STREAM OVER THE UPPER GREAT LAKES... PRELIMINARY PREFERENCE: A NON-00Z CMC MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN AREA OF HEIGHT FALLS ADVANCING THROUGH THE CENTRAL PLAINS WILL EVENTUALLY WORK THEIR WAY INTO THE MIDDLE MS VALLEY/UPPER MIDWEST WHERE A MERGER WITH THE NORTHERN STREAM WILL OCCUR. THROUGH 31/0000Z...THE MODELS ARE IN REASONABLE AGREEMENT WITH THE EXCEPTION OF THE 00Z CMC WHICH IS A HAIR FASTER ACROSS THE GREAT LAKES REGION. EVENTUALLY THIS DIFFERENCE GROWS IN TIME AS THE SYSTEM BECOMES EMBEDDED IN THE FASTER SOUTHWESTERLY FLOW ALOFT. WHILE THE 00Z ECMWF/UKMET GET A BIT AHEAD OF THE 12Z NAM/GFS WHILE CROSSING NEW ENGLAND...IT APPEARS TO BE WITHIN THE GENERAL ENVELOPE OF SPREAD SO WILL FAVOR A NON-00Z CMC MODEL COMPROMISE HERE. ...LONGWAVE TROF SETTING FROM THE ROCKIES TO THE CENTER OF THE COUNTRY... ...ADVANCING BAROCLINIC ZONE... PRELIMINARY PREFERENCE: THROUGH 01/0000Z: GENERAL MODEL COMPROMISE...THEREAFTER: BLEND OF THE 12Z GFS/06Z GEFS MEAN FORECAST CONFIDENCE: INITIALLY ABOVE AVERAGE...THEN BECOMING AVERAGE OVER THE COURSE OF THE PERIOD...THE PATTERN WILL REALLY BEGIN TO AMPLIFY ACROSS THE WESTERN TO CENTRAL U.S. THIS IS IN RESPONSE TO HEIGHT FALLS MOVING INTO THE PACIFIC NORTHWEST WHICH EVENTUALLY HELPS SHAPE A LONGWAVE TROF ACROSS MUCH OF THE NATIONS MID-SECTION. THROUGH 60 HOURS/SUNDAY EVENING...THE MODELS HAVE A DECENT GRASP ON THE EVOLVING SYNOPTIC PATTERN. THEREAFTER...THE 12Z NAM FAVORS DIGGING A SHORTWAVE A LITTLE MORE AGGRESSIVELY INTO THE MIDDLE MS VALLEY. THE BIGGER DIFFERENCES BY DAY 3 ARE MORE UPSTREAM ALONG THE WESTERN EXTENT OF THE LONGWAVE TROF. THE 00Z ECMWF/ECMWF ENSEMBLE MEAN ARE MUCH MORE EMPHATIC ABOUT DIGGING ENERGY INTO THE PACIFIC NORTHWEST BY MONDAY MORNING VERSUS OTHER MODELS WHICH SHOW LESS AMPLITUDE. THIS IS WELL ILLUSTRATED BY THE 564-DM SPAGHETTI PLOT WITH A MAJORITY OF THE ECMWF ENSEMBLE MEMBERS SHOWING THIS IDEA. NOT QUITE SOLD ON THIS SOLUTION YET SO WILL AWAIT ADDITIONAL 12Z GUIDANCE. FOR NOW...A GENERAL MODEL COMPROMISE IS RECOMMENDED THROUGH 60 HOURS BEFORE GOING TO MORE OF A 12Z GFS/06Z GEFS MEAN BLEND. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER